Devices that convert a fibrous sheet composed of an aggregation of fibers into a nonwoven fabric form or paper-like form using a wet papermaking method are already known. The device for producing this fibrous sheet is equipped with a water squeezing section which squeezes the dispersion medium from a dispersion containing the fibers to generate a web, a drying section which dries the web to generate a fibrous sheet, and a winding section for winding the fibrous sheet (for example, see Japanese Unexamined Patent Application, First Publication No. 2008-274525).
A wire mesh (hereafter referred to as a “fabric sheet”) is provided in the water squeezing section. In the water squeezing section, by running the fabric sheet while discharging the dispersion onto the upper surface of the sheet, thereby separating the dispersion medium through the pores in the fabric sheet, the dispersion medium is squeezed from the dispersion to generate a web.
However, in recent years, in the development of fibrous sheets, a reduction in the pore diameter and an increase in the porosity of the fibrous sheet are being demanded.
For example, electrical storage devices such as batteries and capacitors exhibit electrical storage performance by moving an electrolyte between a positive electrode and a negative electrode. In order to prevent short-circuits between the positive and negative electrodes in these electrical storage devices, a separator formed from a fibrous sheet is disposed between the positive and negative electrodes.
Here, in order to improve the electrical storage performance of the electrical storage devices, it is necessary to facilitate the movement of the electrolyte while preventing short-circuits between the positive and negative electrodes. In order to prevent short-circuits between the positive and negative electrodes, a reduction in the pore diameter is required for the fibrous sheet that constitutes the separator. Further, in order to facilitate the movement of the electrolyte, an increase in the porosity is required for the fibrous sheet that constitutes the separator.
Reducing the pore diameter and increasing the porosity of the fibrous sheet is achieved by producing a fibrous sheet using fine fibers. For example, nanofiber cellulose or the like is used as the fine fibers.